OFFSET
1,1
COMMENTS
The identity (441*n + 1)^2 - (441*n^2 + 2*n)*21^2 = 1 can be written as a(n)^2 - A158321(n)*21^2 = 1. - Vincenzo Librandi, Jan 24 2012
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..10000
Vincenzo Librandi, X^2-AY^2=1
E. J. Barbeau, Polynomial Excursions, Chapter 10: Diophantine equations (2010), pages 84-85 (row 15 in the first table at p. 85, case d(t) = t*(21^2*t+2)).
Index entries for linear recurrences with constant coefficients, signature (2,-1).
FORMULA
G.f.: x*(442-x)/(1-x)^2. - Vincenzo Librandi, Jan 24 2012
a(n) = 2*a(n-1) - a(n-2). - Vincenzo Librandi, Jan 24 2012
MATHEMATICA
LinearRecurrence[{2, -1}, {442, 883}, 50] (* Vincenzo Librandi, Jan 24 2012 *)
PROG
(Magma) I:=[442, 883]; [n le 2 select I[n] else 2*Self(n-1)-Self(n-2): n in [1..50]];
(PARI) for(n=1, 38, print1(441*n+1", ")); \\ Vincenzo Librandi, Jan 24 2012
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Vincenzo Librandi, Mar 16 2009
STATUS
approved